There are a couple points to consider of the second amendment to support the argument that the ordinary John and Mary can carry a gun.
Back in colonial times America was basically an agricultural society. There were no Frys-Kroger or Save-Ways to buy food or large cattle yards. If you wanted some meat for dinner you had to go out and shoot it.
Also some of the Americans lived in or were near Indian territory and felt threaten by them. I am sure the Indians felt the way.
No doubt the Founding Fathers knew all this and more and is why they wrote the Second Amendment the way they did.
Ideally, it would be better if there were no guns around anywhere then the bad guys couldn't get them, but we don't live in an ideal society.